vendredi 18 mars 2016

From the bare minimum

Can too much relatedness affect the fate of pioneers?

In a previous post, we spoke about how brown trout managed a rather successful colonization of the remote sub-Antarctic Kerguelen Islands. We also believe that multiple introductions in different river systems and from different origins in Europe increased the probability of success in this process (Lecomte et al. 2013). The general idea behind this belief is that more diversity allows for faster adaptation over generations (or simply allows to select the most adapted genotype at introduction). This well accepted idea in evolutionary biology and in invasion biology can also be looked the other way around: a total lack of genetic variation should actively prevent selection, and thereby possibly prevent adaptation, persistence, and further successful colonization. Think of two genitors, one male, one female, arriving together in a virgin river, and mating there for the first time: the river is initially (and possibly eventually) populated in the most inbred way: brothers and sisters. That means, hell of a low genetic diversity. But it could actually be a frequent case during a colonization process.

A map of Kerguelen Islands where we can observe that much of the eastern parts have been colonized. Our two populations of Val Travers and Clarée, however, are located on the western colonization front.

It is not easy to actually monitor such things naturally, one has to be very lucky to be there, at the right place, at the right time. Although such a luck may sometimes occur, we have another way to look at such a scenario: in the colonization process of Kerguelen, some remote sites were introduced by man as late as 1993, and for two of them, Val Travers and Clarée, we have the initial number of parents that were used to generate the progenies for introduction (one female and one male for Val Travers, one female and two males for Clarée). These two systems have another characteristic: they are still far away from other colonized rivers, and so we can be fairly certain that no immigration occurred yet.